The binding and elution of spleen cells from plastic dishes coated with monophosphoryl lipid A (MPL) resulted in a >1,000-fold enrichment of antigen-specific suppressor T cell (Ts) activity when spleen cells taken from mice 18-24 hr after exposure to a low dose of Type Ill pneumococcal polysaccharide (SSS-III) were used. The removal of MPL-adherent Ts cells resulted in an increase in the degree of amplifier T cell (TA) activity present in the remaining MPL-nonadherent cell fraction; however, both Ts and TA activities were found in the MPL-adherent cell fraction when spleen cells from mice 4 days after immunization with an optimal dose of SSS-III were examined. These findings, as well as others, suggest that both Ts and TA -once activated - acquire a cell surface receptor that enables them to bind to MPL. Because of differences in the kinetics for the activation of Ts and TA during the course of the antibody response and the fact that Ts - but not TA - activity appears as early as 18-24 hrs after exposure to SSS-III, it is possible to use this experimental approach to obtain cell suspensions greatly enriched in Ts activity.